Photoreceptors using an inorganic photosensitive material such as selenium, zinc oxide, or cadmium sulfide were popularly used for copiers and laser printers, but now organic photoreceptors (OPC) using an organic photosensitive material are popularly used therefor because of having advantages over the inorganic photoreceptors such that environmental burdens can be reduced, costs are relatively low, and designing flexibility is relatively high. At the present time, the share of such organic photoreceptors in electrophotographic photoreceptor market is close to 100%. Since environmental preservation is promoted recently, it is desired that such electrophotographic photoreceptors are changed from a supply good (i.e., a disposable good) to a mechanical part (a good having high durability).
Various attempts to impart high durability to organic photoreceptors have been conventionally made. At the present time, a photoreceptor (disclosed, for example, by JP-2000-66424-A) in which a crosslinked resin layer is formed as an outermost layer thereof, and a photoreceptor (disclosed, for example, by JP-2000-171990-A) in which a sol-gel hardened layer is formed as an outermost layer thereof have a high degree of expectation. The former photoreceptor has an advantage such that even when a charge transport material is included in the outermost layer, problems such that the outermost layer is broken or cracked are hardly caused, and thereby the yield of the photoreceptor in the production process can be enhanced. Particularly, by using a radically polymerizable acrylic resin for the outermost layer, the resultant photoreceptor has a good combination of mechanical strength and photosensitivity. Since the crosslinked outermost layers of the above-mentioned two kinds of photoreceptors are formed by plural chemical bonds, a problem such that the outermost layer becomes abradable is not caused even when part of the chemical bonds is cut by a stress.
Recently, it is strengthened to control the amount of emission of carbon dioxide to protect the global environment, and therefore electrophotographic photoreceptors should be changed from a supply good to a mechanical part, and preferably to a reuse part. However, at the present time, electrophotographic photoreceptors have almost the same life as those of mechanical parts, but are not a reuse part having a longer life than the image forming apparatus for which the photoreceptors are used.
The durability of a photoreceptor is expected to be dramatically enhanced by forming a three-dimensional crosslinked structure on the surface of the photoreceptor.
In addition, coating a lubricant on a surface of a photoreceptor is performed for enhancing the cleaning property of toner (particularly, polymerized toner). The lubricant coating is also performed for protecting the photoreceptor from hazards from charging, and therefore contributes to prolongation of the life of the photoreceptor and the image forming apparatus.
However, even when these techniques are used in combination for a photoreceptor, the photoreceptor is used while sometimes replaced with a new photoreceptor at the present time. This is because the properties of the surface of a photoreceptor change after the photoreceptor is repeatedly used, thereby forming abnormal images and deteriorating the cleaning property of the photoreceptor.
Therefore, the life cycle of an image forming apparatus of from obtainment of raw materials of parts of the image forming apparatus, to disposal of the parts after repeated use, and recycling of some of the parts cannot be changed. Namely, a large amount of energy used for image formation using such an image forming apparatus and a large amount of carbon dioxide discharged from the image formation cannot be reduced.
Various technologies have been developed to improve the mechanical strength of photoreceptor, but improvement in the mechanical strength is saturated now.